1. Field of the Invention
The present invention relates to a polymer scale preventive agent for preventing the adhesion of polymer scale to the inner wall surfaces and the like of a polymerization vessel during the production of a polymer by polymerizing a monomer containing an ethylenic double bond in a polymerization vessel.
2. Description of the Prior Art
It is already known that when a monomer containing an ethylenic double bond is polymerized, some of the polymer adheres as scale to the inner wall surfaces and the like of the polymerization vessel.
This adhesion of polymer scale becomes more marked as the number of polymerization batches increases, and causes a reduction in the polymer yield, and a lowering of the cooling capabilities inside the polymerization vessel. Furthermore, another problem arises in that polymer scale that has dislodged from the inner wall surfaces of the polymerization vessel can contaminate the polymer, causing a reduction in the quality of the product. The operation of removing polymer scale that has adhered to the inner wall surfaces and the like of the polymerization vessel not only requires a great deal of time and effort, but is also dangerous, as unreacted monomer incorporated within the polymer scale can harm the human body.
Conventionally, in order to prevent the adhesion of polymer scale to the inner wall surfaces and the like of the polymerization vessel during the polymerization of a monomer containing an ethylenic double bond, a method is used wherein a polymer scale preventive agent is applied to the polymerization vessel inner wall surfaces and the stirrer and the like, thus forming a coating. Known examples of this type of polymer scale preventive agent include mixtures of a condensation reaction product of a naphthol and an aldehyde, with an inorganic colloid (and an additional water-soluble polymer compound) (U.S. Pat. No. 5,576,370), and mixtures of a reaction product of sodium hydroxymethanesulfonate and a naphthol, with a polyvinyl alcohol (WO96/39446 and WO97/08210).
However, it has become clear that a polymer scale preventive coating formed using a polymer scale preventive agent disclosed in the above patent reference 1 does not provide a satisfactory polymer scale prevention effect in the vicinity of the gas-liquid interface inside the polymerization vessel, particularly in the case of polymerization reactions conducted at a polymerization temperature of 60° C. or higher. In addition, if the number of polymerization batches reaches a value of 150 batches or more, then the polymer scale adhered in the vicinity of the gas-liquid interface begins to grow, and as the extent of that growth increases, the scale becomes more likely to dislodge and contaminate the product polymer, causing fish eyes within the polymer product.
Furthermore, as the number of polymerization batch repetitions increases, the polymer scale preventive agent is typically reapplied to the internal surfaces and the like of the polymerization vessel, and as a result, the scale preventive agent layer grows gradually thicker, and portions of the layer can separate and contaminate the product polymer, causing discoloration problems such as the appearance of colored particles within the polymer product, or yellowing of the product following molding. This phenomenon is known as initial discoloration.